SPID#: 8 A STLV-1 related isolate from a baboon is used for vaccine studies. The gene fragment encoding the envelope glycoprotein was cloned into an eukaryotic expression vector (pcDNA1-Amp, Invitrogen). Before using it as a DNA vaccine, we wished to characterize the gene structure and expression. Using Sequence version 2 (USB), the envelope gene was sequenced and its relatedness with known HTLV-1 and STLV-1 isolates was compared. Interestingly, the sequence of the envelope gene of this isolate under study was found to exhibit a high level of sequence identity (97% and 98% respectively at the nucleotide and the amino acid level) to HTLV-1. On the other hand, it was less closely related to STLV-1 (88% at the nt. level and 93% at the amino acid level). Based on the unique sequence of the envelope gene, we have therefore concluded that we have obtained a novel baboon T-cell leukemia virus. The expression, glycosylation, proteolytic processing, cellular localization and cell surface delivery of the expressed glycoprotein were analyzed using a recombinant vaccinia-based transient expression system. These analyses reveal the functional properties of the envelope as well as the prospects of using the plasmid DNA encoding the env gene in subsequent DNA immunization studies. The envelope precursor was synthesized as a 62-66 kd protein, which is presumably cleaved in to gp46, the extracellular component and gp21, which provides the anchoring function. Although the antiserum analyzed in these assays was not able to immunoprecipitate the cleavage products, envelope products can be detected on the surfaces of transfected cells as well as on the CEMss cell line established from the infected baboon. In addition, the envelope gene as well as a fragment which should code for a soluble form of the envelope protein are being cloned into several other expression vectors, and their efficiency in protein expression and generation of an immune response are under evaluation. Infections of macaques with the 1621 virus isolate also have been conducted. For these studies we inoculated three macaques intravenously and three intravaginally with 107 infected cells. This was not enough to induce an infection, but did induce an immune response. Repeated infections using greater amounts of cells did not result in infection in these same animals, presumably because of the immune response from the initial challenge. Inoculations of new animals using the 1621 virus, as well as using two additional STLV-1 isolates recently obtained from the AIDS Reagent Respiratory are underway.